In the art of continuous vertical casting of solid or tubular bar products, it is conventional to provide the external surface of one of the graphite casting dies with a taper and to seat the die in a metal cooler assembly which has a tapered internal passage receiving the tapered surface of the die. Such an assembly, for example, is shown in my U.S. Pat. No. 4,000,773, issued Jan. 4, 1977 and entitled "Die Assembly For Continuous Vertical Casting Of Tubular Metallic Products." The function of the cooler assembly is to withdraw heat from the die which is subjected to extremely high temperatures from the molten material being utilized to form the casting. In order to obtain maximum heat transfer between the cooling assembly and the die, it is important that the engaging tapered surfaces of these parts are continuous and complete contact with each other. The problem presented by the latter objective is to provide matching or complementary tapers on the outer surface of the die and the inner surface of the cooler. Heretofore, this has been accomplished by cutting the tapered surfaces on a lathe utilizing a conventional taper attachment and, to do this, it has been necessary to twice set the lathe cutting tool and lathe attachment with respect to the centerline of the lathe chuck at an angle prior to cutting the tapers on the two parts. This not only slows down the taper cutting process but furthermore subjects the operation to the risk of cutting tapers on the parts which do not exactly correspond. The entire operation relies on the accuracy of the taper attachment and the ability of the operator to set up the tool and attachment accurately. The latter can result in insufficient heat transfer between the die and the cooler which could cause failure of the casting operation. Since the dies are made from relatively expensive material and the set up and preheating before operation consumes time, premature replacement is very costly. It is desirable to be able to make a taper on the female part of the cooler assembly independently of the making of a complementary male die part so that male parts with different die openings can be utilized with the same female part.
In my U.S. Pat. No. 4,151,765 an improved method and apparatus is provided for cutting exactly matching tapers on interfitting male and female parts so as to ensure, when the parts are interfitted, there will be substantially complete and continuous contact throughout the tapered surfaces thereof. In accordance with this patent, a conventional lathe is provided with a revolving chuck at the tail end of the lathe frame which chuck is mounted on a swivel base relative to the lathe bed so as to permit the revolving chuck to be set at a desired taper angle relative to the longitudinal centerline of the lathe. The revolving chuck has multiple jaws which may engage a workpiece externally of the workpiece or internally of the workpiece when the workpiece is a hollow member or sleeve. The revolving chuck is also provided with a suitable motor, for example, an electric motor, for operating the drive shaft to which the chuck is mounted to rotate therewith. In order to cut matching tapers on male and female parts, both of which are sleevelike members, the chuck is adjusted to a desired tapered angle relative to the longitudinal centerline of the lathe; the taper angle corresponding to the angle of the taper to be cut on the parts. One of the parts is then mounted to the chuck of the tail stock and, assuming this part is a male part, the jaws of the chuck extend into the passage of the male part and grip the internal surfaces thereof to hold the part at the desired taper angle. The tool carriage of the lathe and the cross slide and the compound slide thereof which support the cutting tool, are then adjusted to bring the cutting tool into the proper position relative to the external surface of the male part to be cut with the taper. The carriage of the lathe is set to reverse travel. The male part is then rotated by energizing the motor associated with the chuck in one direction and the cutting tool is then moved horizontally along a horizontal path parallel to the centerline of the lathe to cut the desired taper into the external surface of the male part. Upon completion of the tapered surface, the male part is removed from the chuck of the revolving chuck, and the female part is then mounted in the chuck by engaging the chuck jaws with the external surface of the female part. Without changing the angular setting of the cutting tool relative to the longitudinal centerline of the lathe, the cross slide is moved transversely relative to the longitudinal centerline of the lathe to position the cutting tool within the hollow passage of the female part. The motor is then energized to rotate the female part, but in a direction opposite that in which the male part was driven; and the cutting tool is then moved horizontally along the bed of the lathe to cut a taper along the internal surface of the female part. The resulting tapered surface cut on the female part will be at the exact same angle as the tapered surface cut on the male part, however, these surfaces will be complementary to each other so that these parts will interfit, one within the other, along the cut tapered surfaces thereof.
It is a primary object of the present invention to provide an improved method and apparatus for cutting exactly matching or complementary tapers on male and female parts to be interfitted along their tapered surfaces; and which will permit identical but complementary tapers to be cut on male and female parts to be interfitted along their tapered surfaces, with an extremely high degree of accuracy and efficiency and without requiring any special skills from the lathe operator; which apparatus is very economical to build, easy to maintain and operate without skilled labor, does not require taper attachments and which can be used to make a plurality of complementary interfitting parts having high accuracy. Although the present invention is particularly suitable for cutting matching or complementary tapers on a die for continuous vertical casting and an associated cooling sleeve which receives the die, the present invention may well have applicability elsewhere.
In accordance with the invention, the method and apparatus for forming tapered surfaces on male and female parts to be interfitted one within the other along the complementary tapered surfaces thereof which comprises mounting the male part on the chuck of a lathe wherein the chuck axis extends along the centerline of the lathe, positioning a tool on the lathe for movement at predetermined angle to the longitudinal centerline of the lathe, cutting the external surface of the male part to provide a tapered surface by moving the cutting tool along a line extending at said angle while the chuck is rotating in one direction, then removing the male part from the chuck, mounting the female part on the chuck, moving the cutting tool transversely of the lathe without changing the angle of height of the cutting tool, cutting the internal surface of the female part by moving the same cutting tool along a path parallel to the first-mentioned path of the tool while rotating the chuck in the opposite direction.